Described herein are methods for controlling particle growth through the use of complexing agents. More in particular, described are methods of making sulfonated polyester based toner particles, specifically alkali metal sulfonated polyester based toner particles, more specifically bimodal alkali metal sulfonated polyester based toner particles, via emulsion aggregation in which a complexing agent is introduced in order to halt additional aggregation of particles once a predetermined desired particle size is reached.
Small sized toner particles, such as having average particle sizes of from about 3 to about 15 micrometers, preferably from about 5 to about 10 micrometers, more preferably from about 6 to about 9 micrometers, are desired, especially in xerographic engines wherein high resolution is a characteristic. Toners with the aforementioned small sizes can be economically prepared by chemical processes, which involve the conversion of emulsion sized particles to toner composites by aggregation and coalescence, or by suspension, microsuspension or microencapsulation processes.
It has been found that sulfonated polyester resins, and in particular alkali metal sulfopolyester resins, may advantageously be used as the binder material for toner particles. See, for example, U.S. Pat. No. 5,916,725, which describes a process for the preparation of toner comprising mixing an amine, an emulsion latex containing sulfonated polyester resin, and a colorant dispersion, heating the resulting mixture, and optionally cooling.
Illustrated in U.S. Pat. No. 5,593,807, the disclosure of which is totally incorporated herein by reference in its entirety, is a process for the preparation of toner compositions comprising, for example, (i) preparing an emulsion latex comprised of sodio sulfonated polyester resin particles of from about 5 to about 500 nanometers in size diameter by heating the resin in water at a temperature of from about 65° C. to about 90° C.; (ii) preparing a pigment dispersion in water by dispersing in water from about 10 to about 25 weight percent of sodio sulfonated polyester and from about 1 to about 5 weight percent of pigment; (iii) adding the pigment dispersion to the latex mixture with shearing, followed by the addition of an alkali halide in water until aggregation results as indicated, for example, by an increase in the latex viscosity of from about 2 centipoise to about 100 centipoise; (iv) heating the resulting mixture at a temperature of from about 45° C. to about 55° C. thereby causing further aggregation and enabling coalescence, resulting in toner particles of from about 4 to about 9 microns in volume average diameter and with a geometric distribution of less than about 1.3; and optionally (v) cooling the product mixture to about 25° C. and followed by washing and drying.
It has also been recently found that advantageous toner particles may be obtained through the use of binder comprised of a combination of amorphous sulfonated polyester materials, including linear and/or branched polyesters, and crystalline sulfonated polyester materials. See, for example, U.S. patent application Ser. Nos. 10/998,822, filed Nov. 30, 2004, and 11/037,214, filed Jan. 19, 2005, each incorporated herein by reference in their entireties.
As described in the foregoing patent properties, sulfonated polyester materials are most advantageously formed into particles having a size within the desired toner particle size range by the known emulsion/aggregation/coalescence technique. Emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in a number of Xerox patents, the disclosures of which are totally incorporated herein by reference, such as U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,346,797, 5,370,963, 5,344,738, 5,403,693, 5,418,108, 5,364,729, and 5,346,797.
U.S. Pat. Nos. 6,495,302 and 6,582,873, incorporated herein by reference in their entireties, each describe a toner process including, for example, mixing a latex with a colorant wherein the latex contains resin and an ionic surfactant, and the colorant contains a surfactant and a colorant; adding a polyaluminum chloride coagulant; affecting aggregation by heating; adding a chelating component and a base wherein the base increases the pH of the formed aggregates; heating the resulting mixture to accomplish coalescence; and isolating the toner. The latex is described to contain a resin selected from the group consisting of poly(styrene-butadiene), poly(methylstyrene-butadiene), poly(methyl methacrylatebutadiene), poly(ethyl methacrylate-butadiene), poly(propyl methacrylate-butadiene), poly(butyl methacrylate-butadiene), poly(methyl acrylate-butadiene), poly(ethyl acrylate-butadiene), poly(propyl acrylate-butadiene), poly(butyl acrylate-butadiene), poly(styrene-isoprene), poly(methylstyrene-isoprene), poly(methyl methacrylate-isoprene), poly(ethyl methacrylate-isoprene), poly(propyl methacrylate-isoprene), poly(butyl methacrylate-isoprene), poly(methyl acrylate-isoprene), poly(ethyl acrylate-isoprene), poly(propyl acrylate-isoprene), poly(butyl acrylate-isoprene), poly(styrene-propyl acrylate), poly(styrene-butyl acrylate), poly(styrene-butadiene-acrylic acid), poly(styrene-butadiene-methacrylic acid), poly(styrene-butadiene-acrylonitrile-acrylic acid), poly(styrene-butyl acrylate-acrylic acid), poly(styrene-butyl acrylate-methacrylic acid), poly(styrene-butyl acrylate-acrylononitdle), and poly(styrene-butyl acrylate-acrylononitrile-acrylic acid). Polyester resins, much less sulfonated polyester resins, are not described.